Friction Performance Research Articles

Bioinspired film-terminated ridges for enhancing friction force on lubricated soft surfaces

Enhancing friction force in lubricated, compliant contacts is of particular interest due to its wide application in various engineering and biological systems. In this study, we have developed bioinspired surfaces featuring film-terminated ridges, which exhibit a significant increase in lubricated friction force compared to flat samples. We propose that the enhanced sliding friction can be attributed to the energy dissipation at the lubricated interface caused by elastic hysteresis resulting from cyclic terminal film deformation. Furthermore, increasing inter-ridge spacing or reducing terminal film thickness are favorable design criteria for achieving high friction performance. These findings contribute to our understanding of controlling lubricated friction and provide valuable insights into surface design strategies for novel functional devices.

Research on Friction Performance of Friction Stir Welding Tools Based on Non-Smooth Structure.

In this study, based on the principles of bionics, we fabricated a bionic non-smooth concave pit structure on the shoulders of friction stir welding tools and detected the thermal cycling curve, downforce, and torque of the tool in the welding process. We tested the wear loss weight and analyzed the surface morphology of the shoulder surfaces after welding for 200 m. This study found that as the distance between the concave pits decreased and the number of concave pits increased, the maximum downforce, torque, and temperature in the welding process showed a decreasing trend. As the speed increased, no matter how the tool structure changed, the downforce and torque decreased, while the peak thermal cycle temperature increased. The experimental welding results show that the wear loss weight of the non-smooth structure tool significantly reduced. The lowest wear loss weight of the tool with a concave pit interval of 1.125 mm was only 0.1529 g, which is 27% lower than that of the conventional tool. Our observations of the surface morphology of the tool shoulder after welding showed that the amount of aluminum swarf on the tool shoulder of the welding tool gradually declined with the increasing density of the uneven pits. The lowest number of aluminum chips adhered to a welding tool with a pit distance of 1.125 mm. Therefore, friction stir welding tools with biomimetic structures have better wear resistance and adhesion resistance.

Enhancement of mechanical and tribological performance of Ti–6Al–4V alloy by laser surface alloying with Inconel 625 and SiC precursor materials

This study focused on producing metal matrix composite (MMC) coatings on Ti–6Al–4V alloy through laser surface alloying using a novel combination of Inconel 625 and SiC precursor materials. Various ratios of alloying powders were examined to evaluate surface properties such as microhardness, wear resistance, and friction coefficient, along with analyzing the phase composition and microstructure of the coatings. The in situ synthesized MMC coatings exhibited the presence of α-Ti, NiTi, NiTi2, and TiC phases. Additionally, Ti5Si3 and α-Ti/Ti5Si3 eutectic structures were observed when the SiC content exceeded 20%. In comparison to the titanium substrate, the MMC coating significantly enhanced microhardness by over threefold and reduced wear by 95%. However, it was crucial to carefully select the appropriate combination of alloying powders to avoid a substantial decrease in friction performance and excessive formation of cracks. Through a comparative analysis of experimental results, the optimal precursor material composition was identified as 85% Inconel 625 and 15% SiC. This study demonstrated the effective utilization of Inconel 625 and SiC alloying materials to enhance the surface properties of titanium alloys, thereby expanding their application in challenging environments.

Enhancing Lubrication Performance of Plastic Oil Lubricant with Oleic Acid-Functionalized Graphene Nanoplatelets and Hexagonal Boron Nitride Solid Lubricant Additives

The study explored the viability of using waste plastic oil (PO) as an alternative lubricant to petroleum-based lubricants in industrial settings. To enhance the lubrication performance of the PO, this study incorporated cost-efficient, oleic acid-modified, graphene nano platelets [GNP (f)] and hexagonal boron nitride [hBN (f)] nano solid lubricant additives into the PO in various concentrations, forming functionalized nano lubricants. The PO and its functionalized nano lubricant’s rheological, dispersion stability, thermal degradation, friction, and wear performance were investigated. Results manifest that incorporating GNP (f) and hBN (f) into the PO significantly enhanced the viscosity and dispersion stability. In addition, it was seen that GNP (f) and hBN (f) nano lubricants lowered the coefficient of friction (COF) by 53% and 63.63% respectively, compared to the PO. However, the GNP (f) and hBN (f) nano lubricants demonstrated a 3.16% decrease and a 50.08% increase in wear volume relative to the PO. Overall, the GNP (f) and hBN (f) nano lubricants displayed a synergistic friction behavior, while they exhibited an antagonistic behavior pertaining to the wear volume. The study elucidated the mechanisms underlying friction and wear performance of the nano lubricants.

Friction and Wear Performance of a Hydraulic Motor Roller/Piston Pair Contact lined with the Self-Lubricating Bearing Bush Modified by PEEK

Poly Ether Ether Ketone (PEEK) is a kind of special engineering plastic with excellent properties such as high-temperature resistance, self-lubrication, wear resistance, and high mechanical strength. However, its blending or composite modification applications still face numerous challenges. The primary objective of this research was to evaluate the friction and wear performance of a three-layer self-lubricating bearing bush, which was made from a modified material containing short carbon fiber and Poly Ether Ether Ketone (SCF/PEEK). The bearing bush is used as a surface contact layer on the pistons of a hydraulic motor in the interface with the cam roller. The bearing bush was processed using a 15% SCF-modified PEEK material, and the friction and wear test was conducted using a self-built friction test machine. This study aimed to assess the frictional and wear characteristics of the SCF/PEEK-modified material in the bearing bush. The results show that as the experimental pressure rises from 15 MPa to 25 MPa, the friction coefficient of the SCF-modified bearing bush experiences a significant decrease from 0.420 to 0.296. Furthermore, the stability of the frictional morphology of carbon fibers indicates its effective adaptability to low speed and high load conditions.

Extremely enhanced friction and wear performance of hydrogen-free DLC film at elevated temperatures via Si doping

Hydrogen-free diamond-like carbon (DLC) films have garnered significant attention as a highly efficient solid lubrication material, but poor high-temperature lubrication and wear resistance limit their further application. Here, silicon-doped DLC (Si-DLC) films with different Si contents were deposited using a superimposed HiPIMS-DCMS deposition system to improve their high-temperature lubrication and wear resistance performance. The influence of Si content on the microstructure, mechanical and high-temperature friction and wear behavior of Si-DLC films was investigated. The results showed that Si-DLC films had a dense structure and nanoscale smooth surface. The Si doping enhanced the adhesion strength and relieved the residual stress of Si-DLC films, but decreased the hardness and Young's modulus. Meanwhile, Raman and XPS spectroscopy revealed significant local structural changes in Si-doped DLC films. Furthermore, the results showed that DLC films doped with low Si content displayed excellent tribological performance at elevated temperatures due to the graphite lubricating layer on the surface of wear marks. Specifically, Si-DLC film with 3.31 at% Si had an ultra-low average friction coefficient of 0.04 at 450 °C and still provided effective lubrication at temperatures up to 500 °C. In contrast, pure DLC film failed to lubricate at 450 °C due to the severe graphitization transition and Si-DLC film with 17.47 at% Si quickly failed to lubricate at 200 °C due to the SiC and SiO2. This work sheds light for the high-temperature application of DLC films doped with low Si content by superimposed HiPIMS-DCMS deposition system.

Influence of the friction and wear performance of TiB2/7075 aluminum-based composite materials prepared by friction stir processing

Aluminum-based composite layers with different TiB2 contents were prepared by implanting TiB2 reinforcement powders with mass fractions of 1%, 3%, 5%, and 7% into 7075 aluminum alloy sheets using Friction Stir Processing (FSP) technique. The influence of TiB2 content on the friction and wear performance of the modified aluminum-based composite layers was investigated. The results showed that the incorporation of TiB2 reinforcement powders can reduce the friction coefficient and wear volume of the materials, thereby improving the friction and wear performance. Moreover, as the mass fraction of TiB2 reinforcement powder increases, the overall friction coefficient and wear volume of the composite materials exhibit a gradual decrease trend, with adhesive wear being the predominant wear mechanism.

Tribological modifications of water flow at liquid–solid interface by nanobubbles

Previous studies investigated on friction reduction at the solid–liquid interface due to the presence of metal nanoparticles and fine bubbles such as microbubbles. This paper experimentally investigated how nanobubbles (ultrafine bubbles) change the tribological nature of water flow at the solid–liquid interface. We flowed air nanobubbles-containing water into a cylindrical cell filled with soda-lime glass, alumina, and high-carbon chromium-bearing steel beads. We then estimated the changes in the ratio of Darcy's friction factor of nanobubbles-containing water flow (fnb) to that of water flow before injecting nanobubbles (fref) with the time of injecting nanobubbles. We found that nanobubbles are capable of reducing the friction in water flow running through the soda glass beads, accounting for up to 6.1% reduction in terms of Darcy's friction factor ratio (fnb/fref) in our experiment. The magnitude of friction reduction by nanobubbles can be greater with a larger total surface area where surface nanobubbles are present. In contrast, nanobubbles encouraged enhancement of the friction of water flow within the high-carbon chromium-bearing steel beads, showing 3.8% enhancement in the friction factor ratio (fnb/fref). The results indicate that nanobubbles play a role in the friction reduction of water flow when the surface of the bead material is rougher than the size of nanobubbles, while nanobubbles enhance the friction of water flow when the bead surface is smooth enough. Therefore, nanobubbles can be a green nanoscopic additive for modifying the friction and lubrication performance of water flow depending on the surface roughness of the flow material.

The Effects of the Initial Geometrical Errors on the Piston Friction and Sealing Performance in a Buoyancy Regulator of an Underwater Glider

Abstract As an important power component of an underwater glider, the energy consumption of the buoyancy regulator directly affects the endurance of the underwater glider. The accurate calculation and prediction methods for the friction forces can be helpful for improving the working performance of the buoyancy regulator. The traditional friction prediction models consider the cylinder as perfect cylinder without any geometric error, which cannot accurately reflect the effects of the initial geometric defects on the friction force and sealing performance of the cylinder of the piston type buoyancy regulator. This article proposes a new friction force calculation method considering the initial geometrical defects of the cylinder. By using the theoretical analysis and finite element calculations, the effects of the initial geometrical defects on the friction force and sealing performance of the piston type buoyancy regulator can be more accurately analyzed. The effect of the ovality and taper on the friction force and sealing performance is analyzed. In addition, the friction force calculation method proposed in this article is validated by an experiment. This article can provide an accurate cylinder friction force calculation method considering the initial geometrical errors for the piston type buoyancy regulators.

Amino-functionalized Ti3C2 and ZIF-8-induced high lubricity, friction robust self-healing polyurethanes as solid lubrication films

Self-healing polyurethane (SPU) has important applications in areas such as protective coatings, medical devices and solid lubrication. However, improving the lubricating properties of self-healing polyurethanes to reduce their friction and wear is still an important challenge. Herein, an amphoteric SPU is prepared and used as the solid lubrication matrix. NH2-Ti3C2-ZIF-8 is grown on NH2-Ti3C2 in situ to obtain NH2-Ti3C2-ZIF-8 as lubrication additive. The lubrication performance of NH2-Ti3C2-ZIF-8/SPU composites is the best when the NH2-Ti3C2-ZIF-8 content is 1.00 wt%. The coefficient of friction (COF) is only 0.10, and the wear rate is only 1.315×10−4 mm3/(N·m), which are reduced by 80.4 % and 99.4 % respectively compared with single SPU. By exploring the lubrication mechanism, it is found that NH2-Ti3C2-ZIF-8 participated in producing transfer film during friction, and the excellent lubricity and anti-wear effect of NH2-Ti3C2 and the unique adsorption and rolling effect of ZIF-8 jointly improved the friction performance of the samples. In addition, the composite material can realize rapid healing within 5 min at 75 %RH, 20℃, the self-healing efficiency can reach 84.7 %. Therefore, the SPU containing NH2-Ti3C2-ZIF-8 has potential applications in the field of solid lubricated materials.

Effect of crescent-shaped texture based on different depths and orientations on the frictional properties of cam tappets

The cam tappet friction pair is one of the three major friction pairs in an internal combustion engine, and the surface of the tappet undergoes severe wear during operation. To improve the wear resistance of the cam tappet friction pair during operation, in this study, crescent-shaped micro-textures were prepared on the surface of the tappet material of GCr15 steel by laser machining technique, and the effects of the orientation and depth of the texture on the friction properties of GCr15 steel were studied. The processed test samples were tested and characterized by friction and wear tests, scanning electron microscopy (SEM), 3D morphometry, and EDS. The flow field simulation model of micro-texture was established by using Fluent finite element software. The simulation and experimental results show that the crescent-shaped microtexture prepared on the surface of GCr15 steel can play a certain role in reducing friction and wear resistance, meanwhile orientation and depth of the texture affect the friction performance. In the fluid simulation, the positively oriented texture can produce higher oil film pressure than the opposite texture. When the texture depth is 20 μm, it has a better friction and wear reduction effect, and the friction coefficient decreases by 65.81% compared with that of the untextured surface, and the amount of wear decreases by 74.19%. This is mainly due to the existence of texture in the friction process to reduce the contact area and the shallower depth of texture can produce a larger oil film pressure in the oil lubrication state, so it has better tribological performance. The research data provide a certain reference for the design and optimization of the cam tappet friction pair.

Improving frictional and insulation performance with silica-coated titanium dioxide additives in grease

PurposeThe purpose of this study was to synthesize composite nanoparticles (TiO2@SiO2) via the chemical deposition method and investigate their efficacy as additives in polytetrafluoroethylene (PTFE) lubricating grease. The focus was on examining the frictional and conductive properties of the TiO2@SiO2 grease using a friction tester.Design/methodology/approachComposite nanoparticles (TiO2@SiO2) were synthesized using the chemical deposition method and incorporated into PTFE grease. Frictional and conductive properties were evaluated using a friction tester. Surface morphology and chemical composition of wear tracks were analyzed using scanning electron microscope and X-ray photoelectron spectroscopy, respectively.FindingsIncorporating TiO2@SiO2 at a mass fraction of 1 Wt.% led to a significant reduction in friction coefficient and wear width. The wear depth exhibited a remarkable decrease of 260%, while the contact resistance reached its peak value. This improvement in tribological properties could be attributed to the presence of TiO2@SiO2, where TiO2 served as the core and SiO2 as the shell during the friction process. The high hardness of the SiO2 shell contributed to enhanced load-bearing capacity. In addition, the exceptional insulation properties of SiO2 demonstrated excellent electron-capturing capabilities, resulting in improved friction and insulation performance of the TiO2@SiO2 lubricating grease.Originality/valueThis study demonstrates the potential of TiO2@SiO2 composite nanoparticles as additives in lubricating greases, offering improved friction and insulation performance. The findings provide insights into the design of advanced lubricating materials with enhanced tribological properties and insulation capacity, contributing to the development of more efficient and durable lubrication systems.

Effect of lubricant functional groups on tribological properties of epoxy/graphene composites

AbstractThe functional group in the molecular chain of lubricants is a key factor for a boundary lubricating film, which can further enhance the friction performance by interfacial tribochemistry. In this paper, the tribological behavior of epoxy/graphene (EP/Gra) composites was investigated through varying lubrication conditions, including dry friction, or different lubricants (such as water, hexadecane, oleylamine, and oleic acid). The porosity and Shore hardness (SHD) of the EP composites were significantly improved by the addition of graphene. Results showed that the porosity of the EP/0.75 wt.% Gra composites was reduced by 75.6% and their SHD increased by 5.4 compared with the EP/0.05 wt.% Gra composites. The average coefficient of friction (COF) of the composites was reduced by at least 27.3% under dry friction conditions. For water as lubricant, the EP/0.5 wt.% Gra composite exhibited the lowest COF (0.0455). The EP/0.75 wt.% Gra composite displayed the lowest COF (0.0466) when hexadecane acted as lubricant. By contrast, EP/0.05 wt.% Gra showed the lowest COF (0.0389) with oleylamine as lubricant, and the EP/0.25 wt.% Gra composites gave the lowest COF (0.0433) under oleic acid. The amine group of oleylamine reacted with the EP group to form a hydroxyl group, resulting in a polymer with low friction adhered to the friction interface. Simultaneously, the EP group reacted with the carboxyl group, forming a network of hydrogen bonds with graphene, which reduced the shear stress on the friction interface. Therefore, the functional groups of lubricants have a vital influence on the tribological properties of frictional composites, which may provide a new approach to solving the problem of wear.

Preparation and Performance of a Cr/CrN/TiAlCN Composite Coating on a GCr15 Bearing Steel Surface

In order to enhance the surface properties of GCr15 bearing steel, a TiAlCN coating with a low friction coefficient, high hardness, and excellent adhesion was fabricated. The TiAlCN multilayer coating was deposited onto the GCr15 bearing steel surface using magnetron sputtering technology, and optimal coating parameters were achieved by adjusting the number of layers, sputtering power of the graphite target, and coating duration. The experimental results showed that adding Cr/CrN as a transition layer between GCr15 bearing steel and TiAlCN significantly improved multiple properties of the coating. Adding carbon atoms caused TiAlN to dissolve into a TiAlCN structure, enhancing multiple properties of the coating. With the increase in the sputtering power of the graphite target material, the hardness, friction, and wear performance of the coating showed a trend of first increasing and then decreasing. The hardness of the coating gradually increased with time, and the friction coefficient and wear amount first decreased and then increased. When the sputtering power of the graphite target material was 100 W and the coating time was 4800 s, the coating performance was optimal. The hardness was 876 HV, the friction coefficient was 0.42, the wear amount was 1 × 10−4 g, and the wear rate was 2.8 × 10−6 g/m·N under optimal process parameter conditions.

Preparation of Ti–MoS2 coating and gradient structure via mechanical ball milling to improve the wear resistance of AISI 440C stainless steel bearing balls

Owing to its excellent wear resistance and high hardness, 440C stainless steel is widely used in the manufacturing of bearing steel balls. However, in high-speed and heavy-duty environments, bearing steel balls are prone to wear and failure, which affect their service life. This study focused on 440C stainless steel bearing balls and developed a method for preparing Ti–MoS2 coatings and nano gradient structures on the surface of the steel balls via mechanical ball milling so as to improve their wear resistance. A detailed experimental study regarding the surface microstructure and friction performance of the processed balls was simultaneously conducted. The results demonstrated that the surface of the treated bearing steel ball formed a nano gradient structure and a 4 μm Ti–MoS2 coating. The surface roughness of the treated sample decreased by 9.2% and the surface microhardness (831.9 ± 6.4 HV) increased by 28.93% compared to that of the untreated sample. The friction and wear experiments demonstrated that under a load of 80 N, the wear of the treated bearing steel balls decreased by 51.23% compared to that of the untreated bearing steel balls (9.94 ± 0.41) × 106 μm3. Our findings indicate that preparing Ti–MoS2 coatings and nano gradient structures on the surface of steel balls via mechanical ball milling is an effective approach to improving the friction performance of bearing steel balls.

The impact of dual ceramic components (WC/B4C) on the friction performance of copper-based powder metallurgy friction materials and wear mechanism

The copper-based powder metallurgy friction material, modified with dual ceramic components (WC/B4C), underwent friction experiments paired with custom-made carbon ceramic discs. The overall findings are as follows: The judicious addition of dual ceramic components (WC/B4C) can enhance the mechanical, thermal, and frictional performance of copper-based powder metallurgy friction materials. When the WC/B4C ratio is 5:3, the material exhibits the optimal mechanical, thermal, and frictional properties. B4C and WC, after braking, form friction films of B2O3 and WO3. Additionally, the friction film of copper-based powder metallurgy friction materials can be categorized into an oxide layer, a deformation layer, and a matrix layer. The oxide layer primarily consists of Fe2O3, the deformation layer is mainly composed of WO3 and B2O3, and the matrix layer is primarily composed of CuO and Cu2O. With the increase in the WC/B4C ratio, the primary wear mechanisms of copper-based powder metallurgy friction materials shift from abrasive wear to mild fatigue wear, mild fatigue wear progressing to severe fatigue wear, adhesive wear, and fatigue wear, accompanied by a gradual intensification of oxidative wear.

Enhanced Friction and Wear Performance of 297A-Hybridsteel Carburized Layer through Pre-tempering Optimization

Enhanced Friction and Wear Performance of 297A-Hybridsteel Carburized Layer through Pre-tempering Optimization

Effect of temperature on the tribological behavior of additively manufactured tool materials in reciprocating sliding against cemented carbide

Additive manufacturing (AM) of ferrous alloys has achieved a technological maturity level that allows for the production of high-performance steel components. Among these alloys, tool steels and maraging steels can be used in die manufacturing for different hot forming processes as both materials have good mechanical properties and thermal stability. In recent years, several works have successfully produced these alloys through selective laser melting, focusing on the optimization and characterization of their microstructure and mechanical properties. However, few studies look into the tribological aspects of these newly produced materials and even fewer consider high temperature friction and wear performance. Therefore, there is a need to understand the high temperature tribological response of tool materials produced by additive manufacturing. In this context, the aim of this work is to investigate the tribological behavior of a tool steel and a maraging steel, both produced by selective laser melting, at different elevated temperatures. A conventionally produced tool steel was used as reference. A reciprocating sliding tribometer was used to perform tests at 40 °C, 200 °C and 400 °C. The counter-body was a WC-Co cemented carbide. Friction and wear of the AM tool steel and reference tool steel were very similar, thus no signs of the AM route having an impact on the tribological behavior were observed. Both tool steels showed reduced wear volume with increasing temperature, while the opposite was observed for their respective WC-Co counter-bodies. Higher temperature also resulted in increased amount of W transferred onto the tool steel wear scars. AM maraging steel showed higher and more unstable friction level, as well as a much larger wear volume at all temperatures; material transfer onto WC-Co was observed at certain temperatures. Overall, tribolayer formation (or lack thereof) was the dominant aspect in the tribological responses.

Advanced Applications of Porous Materials in Triboelectric Nanogenerator Self-Powered Sensors.

Porous materials possess advantages such as rich pore structures, a large surface area, low relative density, high specific strength, and good breathability. They have broad prospects in the development of a high-performance Triboelectric Nanogenerator (TENG) and self-powered sensing fields. This paper elaborates on the structural forms and construction methods of porous materials in existing TENG, including aerogels, foam sponges, electrospinning, 3D printing, and fabric structures. The research progress of porous materials in improving TENG performance is systematically summarized, with a focus on discussing design strategies of porous structures to enhance the TENG mechanical performance, frictional electrical performance, and environmental tolerance. The current applications of porous-material-based TENG in self-powered sensing such as pressure sensing, health monitoring, and human-machine interactions are introduced, and future development directions and challenges are discussed.

Electric Potential Controlled Ionic Lubrication

Electric potential controlled lubrication, also known as triboelectrochemistry or electrotunable tribology, is an emerging field to regulate the friction, wear, and lubrication performance under charge distribution on the solid–liquid interfaces through an applied electric potential, allowing to achieve superlubrication. Electric potential controlled lubrication is of great significance for smart tunable lubrication, micro-electro-mechanical systems (MEMS), and key components in high-end mechanical equipment such as gears and bearings, etc. However, there needs to be a more theoretical understanding of the electric potential controlled lubrication between micro- and macro-scale conditions. For example, the synergistic contribution of the adsorption/desorption process and the electrochemical reaction process has not been well understood, and there exists a significant gap between the theoretical research and applications of electric potential controlled lubrication. Here, we provide an overview of this emerging field, from introducing its theoretical background to the advantages and characteristics of different experimental configurations (including universal mechanical tribometers, atomic force microscopes, and surface force apparatus/balances) for electric potential controlled lubrication. Next, we review the main experimental achievements in the performance and mechanisms of electrotunable lubrication, especially using ionic lubricants, including electrolyte solutions, ionic liquids, and surfactants. This review aims to survey the literature on electric potential controlled lubrication and provide insights into the design of superlubricants and intelligent lubrication systems for various applications.